1. Field of the Invention
The present invention relates to a motor vehicle with a first powertrain including an engine and a second powertrain including an electric traction motor, and more particularly to apparatus and method for providing protection to an electric traction motor of a motor vehicle.
2. Description of the Background Art
Motor vehicles are proposed, which have a first powertrain including an engine, and a second powertrain including an electric traction motor. The first powertrain is coupled with a first set of road wheels. The second powertrain is coupled with a second set of road wheels. Various examples of a motor vehicle of the above kind are known from JP-B2 P3062721, JP-B2 P3261673 (=U.S. Pat. No. 6,008,606) and JP-A 11-243608, respectively.
A motor vehicle disclosed in JP-B2 P3062721 includes an electric traction motor and a reduction gearing. The reduction gearing is connected to a clutch to engage and disengage the motor to and from the associated road wheels. The motor is excited only for assisting start-up of the motor vehicle. The excitation of the motor ends when the load on the motor drops after a temporary rise. When the excitation of the motor ends, the clutch disengages the motor from the road wheels.
A motor vehicle disclosed in JP-B2 P3261673 (=U.S. Pat. No. 6,008,606) includes an electric traction motor and a reduction gearing. The reduction gearing is connected to a dog clutch to engage and disengage the motor to and from the associated road wheels. The motor is excited only for assisting start-up of the motor vehicle. The excitation of the motor ends when the load on the motor drops after a temporary rise. When the excitation of the motor ends, the clutch disengages the motor from the road wheels. A sensor is provided to detect whether or not engagement of the dog clutch is released. The dog clutch may remain engaged due to application of torque from the road wheels. When the sensor output indicates that the dog clutch remains engaged upon wheel speed exceeding a predetermined speed value after the vehicle has started, the torque applied to the dog clutch is offset by exciting the motor to rotate in one and the opposite directions momentarily.
A motor vehicle disclosed in JP-A 11-243608 includes an electric traction motor and a reduction gearing. The reduction gearing is connected to a clutch to engage and disengage the motor to and from the associated road wheels. To avoid shocks, according to one control strategy, the motor is controlled to raise output torque gradually after engagement of the clutch. According to another control strategy, the motor is controlled to increase speed up to a speed value that is calculated in motor speed of a wheel speed value of the road wheels immediately before engagement of the clutch.
In application to the motor vehicles, electric traction motors need to be inexpensive, compact and light. There is an allowable upper limit, in rotation speed, of each electric traction motors of the above kind. The allowable upper limit is permitted for steady operation of the motor.
In the above-mentioned applications, a clutch engages an electric traction motor to the associated road wheels, and a reduction gearing transfers the motor power to the associated road wheels. The provision of such reduction gearing permits the electric traction motor for operation at sufficiently high speeds for torque output required when the vehicle operates in predetermined operating areas. The clutch disengages the motor from the associated road wheels when the vehicle operates outside of the predetermined operating areas. Monitoring the clutch is needed to provide a safeguard against possible occurrence of a situation. Such situation occurs if the clutch should continue to engage, completely or partially, the motor to the associated road wheels when the vehicle operates outside of the predetermined operating areas. Under this condition, the associated road wheels might force the motor to turn above the allowable upper limit. In the prior art, a sensor such as a stroke sensor is proposed. However, the provision of such additional sensor results in a cost increase.
A need remains for apparatuses and methods, which provide protection to an electric traction motor of a vehicle.
It is thus an object of the present invention to provide apparatus and method for providing protection to an electric traction motor of a motor vehicle.
Another object of the present invention is to provide apparatus and method for providing protection to an electric traction motor of a motor vehicle without any additional sensor that is designed for monitoring a clutch.
Another object of the present invention is to provide apparatus and method for enabling a motor vehicle to continue running if a clutch remains engaged while providing protection to an electric motor.